At the main menu or while playing the game, press Up, Up, Down, Down, Left, Right, Left, Right to unlock the "Relive Episode" option, which allows you to select any level including those that have not yet been played. If you entered the code correctly, you will hear a sound.

Infinite ammunition

At the main menu or while playing the game, press Up, Down, Left, Right, Up, Down, Left, Right. If you entered the code correctly, you will hear a sound.

Watermark 20

At the main menu or while playing the game, press Z, Z, Z, C, Z, Z, C, C, Z. If you entered the code correctly, you will hear a sound and "Watermark 20" text will be displayed. The full effect of this code remains unknown.

Relive Scene option

Successfully complete the game to unlock the "Relive Scene" option. This option allows any level to be replayed, including the "Release Therapy" bonus level.

Bonus level

Successfully complete the game to unlock a bonus level with Leo.

Familiar face

Go to the door where the guard tells you he will not let you in because you are not a familiar face. Turn around, go off the stage, and climb up the steps on your left. Then, go up the stairs on that side. Move up the stairs until reaching the top. On the right side down the hallway is a case on the wall. Inside the case is an axe. Use the axe on a person or body. Executions immediately detach a head, where as hacking at a corpse requires a few swings. Pick up the head. Run back to the door, and equip the head as a weapon. Go to the door, and press Action. The guard will now let you in.